J-head with ceramic body instead of PEEK

Hi guys, I just wanted to show you something I found on the web today while looking for a J-head:
[www.2engineers.com]

Would this work well do you think? They live in Belgium, so for me it's pretty close (Holland). Their geared stepper is also quite affordable.

Anyone has experience with this ceramic zirconium insulator?

i think this is the way to go if you arent water cooling. ive experimented a little with some graphite but its actually fairly conductive with heat still, although not as much as metal.

Although ceramic, the upper temperature is still limited by the PTFE liner which has a max of 260 deg C. Using PEEK is OK for printing ABS.
We need a hot end that can print all plastics regardless of temp.

To be honest, I'm doubting the plus value of this thing. And I really don't get what they mean with that you don't need kapton to fix the ceramic heater and thermistor?

actually ptfe can be used up to about 285, and this is much better than peek because the peek was a structural component in the hot end. I bet a high temp silicone tube would work pretty well in the place of ptfe.

I did not know ptfe went that high. What we want is a material that has low thermal conductivity and high structural strength at high temps. Why not just solid ptfe? I must admit I do not know enough about hotend design.

If I were building my own hotend, I'd connect a PTFE tube straight to a brass heater block + nozzle (like a bowden tube that goes all the way up to the brass part of a j-head, but without any "structural" PEEK that insulates the PTFE from cooling). Outside of that, a few smaller ~M3 sized screws to hold the nozzle in place. They would attach to an aluminum mount/heat spreader at the carriage.

I think all of these structural components surrounding the PTFE liner (PEEK, ceramics) are totally unnecessary and are working against you. You don't want to further insulate the PTFE. Keep the melt zone short and entirely in the brass part.

Edited 1 time(s). Last edit at 01/15/2014 05:53PM by iquizzle.

Well, it's nice to think about materials. I have been playing with 2-component PU-materials. Making castings with all kinds of different things. Ofcourse, this is not usable for a 3D-printer, but I'm pretty sure that there must be a material that can withstand heat, and still not become very toxic at the same time. I think thats one of the reasons why they use PEEK and PTFE. Low toxicity with the usual printing temperatures.

To be honest, I'm still under the impression that the E3D kind of hotends will be the future.

I thought about why not just a solid block of ptfe? the same shape as the peek jhead.
Must be a reason why not.

Quote
dave3d
I thought about why not just a solid block of ptfe? the same shape as the peek jhead.
Must be a reason why not.

Even at 5/8" or whatever the diameter of the jhead is, PTFE is still pretty flexy. Not great for making threads either.

There's no reason to believe that the hotend supports have to surround the PTFE liner. It's a bad idea and not the best design to do it that way. All of the channels in the PEEK part of the j-head are trying to compensate for the fact that your PEEK barrel is insulating the PTFE tube. Make structural supports outside the tube that carries the filament. You don't have to increase the heat capacity of the materials surrounding the filament by making them thick. You don't need more than a 1mm PTFE wall to guide the filament into the brass part.

Edited 1 time(s). Last edit at 01/15/2014 06:05PM by iquizzle.

PTFE becomes soft at printing temps so it can't be structural.

My current hot end is basically a Bowden tube attached to the nozzle. The heater block slips on around the nozzle, the nozzle screws onto a piece of stainless that has a hole for the PTFE to go through. The stainless is held between two pieces of phenolic, which is attached to another piece of phenolic with some standoffs. The ptfe tube is cooled just above the stainless piece. Its basically the water cooled version of the sg2. You could probably machine a stainless tube to fit in place of the PTFE if you wanted to go higher than 280

Quote
aduy
PTFE becomes soft at printing temps so it can't be structural.

My current hot end is basically a Bowden tube attached to the nozzle. The heater block slips on around the nozzle, the nozzle screws onto a piece of stainless that has a hole for the PTFE to go through. The stainless is held between two pieces of phenolic, which is attached to another piece of phenolic with some standoffs. The ptfe tube is cooled just above the stainless piece. Its basically the water cooled version of the sg2. You could probably machine a stainless tube to fit in place of the PTFE if you wanted to go higher than 280

Nice! Do you have any pictures? I've been wanting to make something similar to that for a while. Is the water cooling necessary?

yeah ive got a picture, and no for abs the water cooling is not needed but it helps to shorten the transition zone to almost nothing. and for pla thats good.


Edited 1 time(s). Last edit at 01/15/2014 10:50PM by aduy.

Quote
aduy
PTFE becomes soft at printing temps so it can't be structural.

I've found that adding a heat sink effectively mitigates any problems with PTFE at <250C. Ceramic and PEEK are great insulators, but Teflon Is way more cost effective. 1/2" PTFE rod works gangbusters.

as long as the pfte tubing stays structurally stable it should not matter what is on the outside as long as it pulls some heat away.

ceramic parts would need not crack under stress.

I've always wondered, since seeing someone's post about using sodium silicate to patch their hotend, whether it would be usable as a structural component to directly mount the brass into. You can get an exhaust patch kit (like this one [goo.gl]) for $10aus and it appears to have enough strength to handle strenuous loads without issue.

Any feedback on this - or previous experiments along these lines?

I wonder if you could mold a brass nozzle into a piece of glass.

Glass conducts heat too well. The heat from the hotend would be transfered to the x carriage.

I think that would be borate silicate, and it is used to hold things in pace in the hot end, and to keep the seal in a 2 part hot end. it is not used structurally as of yet. I don't think it would work on its own.

Early hot-end designs used PTFE and brass. The PTFE was known to fail rather quickly as PTFE makes a poor support material. PEEK alone was tried and didn't work well with PLA. Next, a hybrid design was tried that used a PTFE sleeve and PEEK body. Fast forward some time and the modern J-Head venting system was developed. The PEEK wall, between the root of the vents and the PTFE liner, is only about 1mm thick. This is to support the PTFE liner while allowing for cooling and preventing heat build-up.

Prior to the PEEK vents, the J-Head Mk III series used an aluminum heat sink. This worked well. However, the heat sink was an additional part to manufacture and install. The venting system allowed for the complete elimination of the heat-sink.

Regards,

Brian

For what it is worth, I am a retired engineer from the chemical industry.
We fabricated parts, bearings, bushes, seals, etc, from filled ptfe for arduous duties.
Rulon was one material we used. I think it is a glass filled ptfe. The mechanical strength is far better than solid ptfe and it is easy to machine. There are many grades but Rulon AR for example will withstand 288 deg C.

[en.wikipedia.org]

Rulon i looked at a while ago, there are plenty of options with it, however the cost of some of these materials can be incredibly high, and in some cases availability is a serious problem, and the difference country to country is borderline criminal in some cases

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Just to be clear, it's Ceramic Zirconium.

My concern was that Zirconium becomes brittle when it is exposed to heat for consecutive long periods of time. I would stay with PEEK.

Rulon might be a good material:
[tetw.org]

Edited 1 time(s). Last edit at 01/26/2014 06:22AM by Ohmarinus.

Quote
Ohmarinus
Just to be clear, it's Ceramic Zirconium.

My concern was that Zirconium becomes brittle when it is exposed to heat for consecutive long periods of time. I would stay with PEEK.

Rulon might be a good material:
[tetw.org]

MgO or Yttria stabilized grades of Zirconium are very stable.
Pure ZrO2 is known to crack, so additives are used to stabilize it.

Key Properties of Zirconium Oxide
Use temperatures up to 2400°C
High density
Low thermal conductivity (20% that of alumina)
Chemical inertness
Resistance to molten metals
Ionic electrical conduction
Wear resistance
High fracture toughness
High hardness

Typical Uses of ZrO2
Precision ball valve balls and seats
High density ball and pebble mill grinding media
Rollers and guides for metal tube forming
Thread and wire guides
Hot metal extrusion dies
Deep well down-hole valves and seats
Powder compacting dies
Marine pump seals and shaft guides
Oxygen sensors
High temperature induction furnace susceptors
Fuel cell membranes
Electric furnace heaters over 2000°C in oxidizing atmospheres

Zirconium oxide
Zirconium oxide is used due to its polymorphism. It exists in three phases: monoclinic, tetragonal, and cubic. Cooling to the monoclinic phase after sintering causes a large volume change, which often causes stress fractures in pure zirconia. Additives such as magnesium, calcium and yttrium are utilized in the manufacture of the knife material to stabilize the high-temperature phases and minimize this volume change. The highest strength and toughness is produced by the addition of 3 mol% yttrium oxide yielding partially stabilized zirconia. This material consists of a mixture of tetragonal and cubic phases with a bending strength of nearly 1200 MPa. Small cracks allow phase transformations to occur, which essentially close the cracks and prevent catastrophic failure, resulting in a relatively tough ceramic material, sometimes known as TTZ (transformation toughened zirconia).

Zirconium dioxide is one of the most studied ceramic materials. Pure ZrO2 has a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at increasing temperatures. The volume expansion caused by the cubic to tetragonal to monoclinic transformation induces very large stresses, and will cause pure ZrO2 to crack upon cooling from high temperatures. Several different oxides are added to zirconia to stabilize the tetragonal and/or cubic phases: magnesium oxide (MgO), yttrium oxide, (Y2O3), calcium oxide (CaO), and cerium(III) oxide (Ce2O3), amongst others.

In the late 1980s, ceramic engineers learned to stabilize the tetragonal form at room temperature by adding small amounts (3–8 mass%) of calcium and later yttrium or cerium. Although stabilized at room temperature, the tetragonal form is “metastable,” meaning that trapped energy exists within the material to drive it back to the monoclinic state. The highly localized stress ahead of a propagating crack is sufficient to trigger grains of ceramic to transform in the vicinity of that crack tip. In this case, the 4.4% volume increase becomes beneficial, essentially squeezing the crack closed (i.e., transformation decreases the local stress intensity).

Edited 1 time(s). Last edit at 01/26/2014 08:54AM by A2.

Quote
dave3d
Glass conducts heat too well. The heat from the hotend would be transfered to the x carriage.

Thermal conductivity:
Diamond thermal conductivity: 1000 W/(m·K).
Copper thermal conductivity: 385 to 401 W/(m·K).
Aluminum: 205 W/(m·K).
Stainless steel 16 W/(m·K).

Granite: 1.7 to 4 W/(m·K).
Zirconia has a typical thermal conductivity of 1.7 to 2.2 W/(m·K).
Porcelain has a typical thermal conductivity of 1.5 to 5 W/(m·K).
Glass thermal conductivity: 1.05 W/(m·K).

[www.engineeringtoolbox.com]

Edited 1 time(s). Last edit at 01/26/2014 09:19AM by A2.

A2, thanks for clearing that up. Ofcourse I had looked up the wrong info, I had only been looking at Zirconium by itself!

Quote
reifsnyderb
Early hot-end designs used PTFE and brass. The PTFE was known to fail rather quickly as PTFE makes a poor support material.

In the early days they used 3mm filament. With 1.75mm filament the forces are less so that ptfe can be used. This with the addition of a stainless steel barrel and a heat sink to prevent the ptfe from overheating makes for a reliable budget hot end.

I think part of the reason ptfe works so well is when it does get hot it actually has more give so if the filament does swell it doesnt jam as much as something that is rigid like metal or ceramic. I think a great unexplored material is actually high temperature silicone, if youve ever taken apart a hot glue gun you will notice that its an extruder that has a metal tube with a silicone tube as the transition zone. the silicone basically just prevents backflow and works excellently. I think people should experiment with silicone as a material instead of ptfe, I bet it would actually slip right into many of the current designs. just from doing a bit of googling ive found that some silicone caulk is good up to 343C, and its easily moldable, you could 3d print the mold for the insert and then just caulk it and crack away the mold once its done.

Edited 1 time(s). Last edit at 01/26/2014 11:43AM by aduy.

ohioplastics ;


PTFE by itself makes a terrible support structure for a hot end. I think above 80C, PTFE becomes somewhat soft. soft enough to slip its own threads on a brass nozzle inserted inside.

if support is added at the very least to the bottom a nut and washer to keep inside threaded brass moving down then that is at least something. I have finished many prints in the old days just to see the old brass hot end slip out. quite frighting considering maintenance used to be custom wire wound ni-crhome and 3 days curing fire cement so the PTFE failure caused down for up to a week as the fire cement curing did not always work perfectly.

however having a PTFE tube with a very strong steel or thick sleeved brass rod sleeve worked quite well. as the PTFE becomes soft it can't slip down, and it wont bulge out because of the support sleeves. it is however cheaper to use peek on the outside.

I'm not using brass, I'm using M6 stainless steel. Look at the thermal conductivity of brass vs stainless steel. Brass 109-121W/(m·K) vs stainless steel 16 W/(m·K). Add a copper heat sink on the tube, and it hasn't come apart at all, especially when you assemble it when it's hot to compensate for thermal expansion. Instead of developing a way to work with a material that is 1/8th the cost of PEEK, people abandoned it. But that was before stainless steel tubes and 1.75mm filament came in vogue. I think it's coming back around and I'm not just saying that because I'm selling it. I believe it's the only way to bring the cost down for everyday working people.